1. Field of the Invention
The present invention relates to an optoelectronic substrate, particularly to a circuit substrate having an electronic device and an optical device in combination.
2. Related Background Art
In recent years, data processing apparatuses such as portable telephones and personal digital assistance (PDA) are required to have a high-speed processing ability, a small size, and a light weight simultaneously. However, with increase of the processing speed, the adverse effect of wiring delay has become remarkable. To prevent the wiring delay, the simplest way is to shorten the wirings inside and between the chips. The wire-shortening is also helpful in miniaturizing the substrate, so that many inventions have been disclosed thereon.
However, the increase of the processing speed has given rise to another problem of electromagnetic radiation interference noise (EMI).
The problem of EMI is explained below.
Shortening of the wiring by close arrangement of the electronic parts increases the wiring density. Consequently, when signals flow in a high speed through adjacent wirings, the electromagnetic waves can interfere with each other to cause noises, preventing precise transmission of the signals. In particular, in mobile terminals, which are coming to be driven at a lower voltage and higher electric current intensity, the adverse effect of the EMI is becoming serious.
The adverse effects can be prevented, for example, by making the ceramic substrate multi-layered to increase the electromagnetic radiation noise immunity (EMC) of the respective layers. However, this is not satisfactory in the production cost and yield.